Enhanced mercury capture from coal-fired power plants in the filtration baghouse using flue gas temperature as process control knob

ABSTRACT

A system and associated method for improved mercury removal from a flow containing combustion exhaust. The system includes a filtration arrangement through which the flow proceeds to remove material, including mercury, from the flow. The system includes a sensor arrangement sensing a mercury concentration within the flow downstream of the filtration arrangement and providing a signal indicative of the sensed mercury concentration. The system includes an adjustable temperature control arrangement changing a temperature of the combustion exhaust proceeding to the filtration arrangement in response to the signal indicative of the sensed mercury concentration to change an amount of mercury being removed from the flow.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to air filtration, and moreparticularly to air filtration that provides for improved fly ash and/ormercury emission control.

2. Discussion of the Prior Art

Air filters are known and used in many different applications, includinguse within filtration arrangements associated with combustion devices,such as coal-fired boilers. The air filters are capable of filteringparticulate matter, such as fly ash, from combustion exhaust.

It is known that some combustion fuels, such as coal, include mercury(Hg). It is desirable to control the amount of mercury proceeding from acombustion device and through an air filter. It is known to add asorbent, such as activated carbon, into the combustion exhaust gas in aneffort to help entrap the mercury and thus remove the mercury from thecombustion exhaust. However, there may be some aspects connected withthe use of sorbent that are disfavorable, such as the cost of obtainingthe sorbent.

In addition to a general desire to entrap mercury, there may also adesire to entrap mercury despite fluctuation of a concentration ofmercury and/or other fluctuations that have an influence on theentrapment of mercury. Examples of such other fluctuations that have aninfluence on the entrapment of mercury may include variations in the flyash in the combustion exhaust, gas chemistry within the combustionexhaust, combustion exhaust gas flow rate, filter media condition (e.g.,deterioration thereof), dust-cake build-up, etc.

It would be beneficial to be able to control mercury entrapment in adesirable manner.

BRIEF DESCRIPTION OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some example aspects of the invention.This summary is not an extensive overview of the invention. Moreover,this summary is not intended to identify critical elements of theinvention nor delineate the scope of the invention. The sole purpose ofthe summary is to present some concepts of the invention in simplifiedform as a prelude to the more detailed description that is presentedlater.

In accordance with one aspect, the present invention provides a systemfor improved mercury removal from a flow containing combustion exhaust.The system includes a filtration arrangement through which the flowproceeds to remove material, including mercury, from the flow. Thesystem includes a sensor arrangement sensing a mercury concentrationwithin the flow downstream of the filtration arrangement and providing asignal indicative of the sensed mercury concentration. The systemincludes an adjustable temperature control arrangement changing atemperature of the combustion exhaust proceeding to the filtrationarrangement in response to the signal indicative of the sensed mercuryconcentration to change an amount of mercury being removed from theflow.

In accordance with another aspect, the present invention provides asystem for improved mercury removal from a flow containing combustionexhaust. The system includes filtration means for removing material,including mercury, from the flow proceeding through the filtrationmeans. The system includes sensor means for sensing a mercuryconcentration within the flow downstream of the filtration means and forproviding a signal indicative of the sensed mercury concentration. Thesystem includes temperature control means for changing a temperature ofthe combustion exhaust proceeding to the filtration means in response tothe signal indicative of the sensed mercury concentration to change anamount of mercury being removed from the flow.

In accordance with another aspect, the present invention provides amethod for improved mercury removal from a flow containing combustionexhaust. The method includes filtering the flow to remove material,including mercury, from the flow proceeding through a filtrationarrangement. The method includes sensing a mercury concentration withinthe flow downstream of the filtration arrangement and for providing asignal indicative of the sensed mercury concentration. The methodincludes changing a temperature of the combustion exhaust proceeding tothe filtration arrangement in response to the signal indicative of thesensed mercury concentration to change an amount of mercury beingremoved from the flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 schematic illustration of an example filtration systemincorporating at least one aspect of the present invention;

FIG. 2 illustrates a side view of an example filter cartridge that canbe used within the system of FIG. 1;

FIG. 3 is an enlarged, cross-sectional view of the filter cartridgetaken along line 3-3 of FIG. 2 and shows an accumulation of particulatematter;

FIG. 4 is an enlarged, cross-sectional view of the filter cartridgetaken along line 4-4 of FIG. 3; and

FIG. 5 is a top level flow chart of an example method in accordance withan aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Example embodiments that incorporate one or more aspects of the presentinvention are described and illustrated in the drawings. Theseillustrated examples are not intended to be a limitation on the presentinvention. For example, one or more aspects of the present invention canbe utilized in other embodiments and even other types of devices.Moreover, certain terminology is used herein for convenience only and isnot to be taken as a limitation on the present invention. Still further,in the drawings, the same reference numerals are employed fordesignating the same elements.

FIG. 1 schematically shows a system 10 for processing combustion exhaustand specifically for providing improved mercury (Hg) removal from theflow that contains the combustion exhaust. The combustion exhaust fromthe source contains particulate matter. The shown example includes afiltration arrangement 12 for filtering particulate from the combustionexhaust. The particulate includes a material that is commonly referredto as fly ash.

Within the shown example, the filtration arrangement 12 includes abaghouse 14. The baghouse 14 may be defined by an enclosed housing 16and can be divided into two sections: a dirty air plenum 18 and a cleanair plenum 20. The dirty air plenum 18 and the clean air plenum 20 maybe placed in fluid communication with each other and separated by atubesheet 22, which is a wall, a divider, or the like. The dirty airplenum 18 is in fluid communication with a dirty air inlet port 26allowing the combustion exhaust flow to enter the baghouse 14 throughthe dirty air inlet port 26. The clean air plenum 20 is in fluidcommunication with a clean air outlet port 28 allowing filtered air toexit the baghouse 14 through the clean air outlet port 28.

The dirty air plenum 18 and the clean air plenum 20 may be arranged influid communication via one or more circular openings formed in thetubesheet 22. Each opening may be sized to accept and hold a filtercartridge 30. Two of the shown filter cartridges 30 are raised off ofthe tubesheet 22 within FIG. 1 to show that the filter cartridges 30 areinserted into the tubesheet 22. The tubesheet 22 prevents the passage ofair through the tubesheet. Instead, air may pass from the dirty airplenum 18 to the clean air plenum 20 through the filter cartridges 30.It is to be appreciated that the filtration arrangement 12 may be variedand specifically the baghouse 14 may be varied. As such, the presentedexample is not to be taken as a limitation upon the present invention.In particular, although filter cartridges are shown, a different type offilter in accordance with an aspect of the present invention may beutilized. Also, although only six filter cartridges 30 are shown, thefiltration arrangement 12 may include any number (i.e., one or more) offilter cartridges 30.

Each example filter cartridge 30 is generally elongate may be arrangedparallel (e.g., axes of elongation) to each other in a substantiallyvertical manner. The filter cartridges 30 are capable of filtering airto remove particulate matter, possibly including fly ash, from thecombustion exhaust.

As shown in FIGS. 2 and 3, a representative example filter cartridge 30includes a filter media 40 in accordance with one aspect of the presentinvention. In the shown example, the filter media 40 is arranged aroundan inner core 42 (FIG. 3). The inner core 42 defines an elongatedcentral passageway 44 formed within the filter cartridge 30. Theelongation is along a center axis 46. The inner core 42 may be made of anumber of different materials, such as steel, titanium, or the like, andmay be sufficiently stiff to provide some support to the filtercartridge 30. The core 42 includes openings therethrough to allow forthe passage of air through the core. For instance, the core 42 mayinclude a plurality of perforations, apertures, holes, etc. to allow airto pass from the exterior of the core to the central passageway 44.

In the shown example (FIGS. 2 and 3), the filter media 40 is arrangedgenerally as a tube to encircle the inner core 42 and has a plurality ofpleats 48. The pleats 48 are elongated parallel to the axis and extentin a zigzag pattern toward and way from the center axis 46. The segmentsbetween the pleat bends are essentially flat segments. The filter media40 has an inner surface 52 and an outer surface 54. In the shownembodiment, a portion of the inner surface 52 engages and/or is adjacentto the inner core 42 at the radially inward extent of the pleats 48.Thus, the core 42 can support the filter media 40 from radial inwardmovement during normal filter flow.

In the shown example, the filter cartridge 30 includes one or moreretaining straps 58 used to hold and/or secure the filter media 40 inplace. For example, the retaining straps 58 limit radially outwardmovement during a cleaning pulse. Such retaining straps may include anumber of materials with a high tensile strength, including an extrudedpolymer, woven polyester, metal, high temperature fabric, etc. Also,such retaining straps may be secured around the circumference of thefilter media in a number of locations, such as at a central positionbetween the bottom and top of the filter cartridge. Similarly, more thanone retaining strap may be provided for securing the filter media, as inthe shown example, two retaining straps are used. It is to beappreciated that other structures may be present on the filter cartridge30.

The filter cartridge 30 may also include one or more end caps 62, 64(upper and lower) at either or both ends of the filter cartridge. Theend caps 62, 64 may act to allow and/or prevent the passage of airthrough an end of the filter cartridge and ensure that flow is onlythrough the filter media 40 to aid the filtering process. The caps mayinclude rigid members, seals, etc. as will be appreciated by the personof ordinary skill in the art. Also in the shown example, the lower endcap 64 provides for complete blocking, whereas the upper end cap 62provides for perimeter sealing and is open at a center to permit airflow out from the central passageway 44.

It is to be appreciated that the filter media 40 may have a variety ofconstructions/compositions. For example, the filter media 40 may includea layer of expanded polytetrafluoroethylene (ePTFE) membrane layer 76.It is to be appreciated that the ePTFE membrane layer 76 may besupported by other structures/layers of the filter media. For example,the filter media may include a media substrate layer 70. The mediasubstrate layer 70 may include a variety of materials and/orconstructions. For example, the media substrate layer 70 may include thefollowing materials: polytetrafluoroethylene (PTFE), polyethylene,polyphenylene sulfide (PPS), and/or glass fibers. Also for example, themedia substrate layer 70 may include a single, mono-material layer,multiple material layers, and/or other structures. It is to beappreciated that the media substrate layer 70 need not be a limitationupon the present invention. An example of particulate matter 80entrapped by the filtration arrangement 12 is on the outer surface 54 ofthe filter media 40. It is to be appreciated that particulate matter 80′(FIG. 1) is generally accumulated within the dirty air plenum 18 of thefiltration arrangement 12 and may be collected for disposition (e.g.,disposal, sale).

Of course, it is to be understood that the shown filtration arrangement,filter, filter media, etc. are just presented as an example. Differencesin the filtration arrangement, the filter, the filter media, etc. arepossible and contemplated. For example, round bag filters could be used.As another example, the filter media may have additional/differentmaterials or/fabrics.

It is to be appreciated that the filtration arrangement 12 has at leastsome ability to remove mercury from the combustion exhaust flow. Suchability to remove mercury may be in combination with the remove of theparticulate matter 80 (e.g., fly ash) from the combustion exhaust flowproceeding through the filter arrangement. The details of themechanism/methodology of removing mercury may be varied and need not bea specific limitation upon the present invention. Some example detailsof mechanisms/methodologies of removing mercury are presented below.

In connection with one example mechanism/methodology of removing mercuryit has been noted that mercury within combustion exhaust is typicallyelemental mercury. Such elemental mercury does have an ability to passthrough some previous types of filter arrangements. However, it shouldalso be noted that the combustion exhaust typically includeshydrochloric acid (HCl). It is theorized the hydrochloric acid withinthe combustion exhaust can collect at the filter element (e.g., filtermedia 40/filter cartridge 30) of the filtration arrangement 12. It isfurther theorized that the hydrochloric acid can oxidize the elementalmercury into mercuric chloride.

It is still further theorized that the presence of the particulatematter 80 provides a substance that captures the created mercuricchloride. Thus, the mercury, which is now if the form of mercuricchloride, is entrapped within the filtration arrangement 12 with theparticulate matter 80 and removed from the combustion exhaust flow. Assuch, the overall amount of mercury that is entrapped by the filtrationarrangement 12 is relatively high. See the example within FIG. 1 whichshows a representative accumulation of the particulate matter 80′, withthe captured mercury, that is accumulated within the dirty air plenum 18of the filtration arrangement 12.

It should be noted that it is possible to introduce a sorbent into thecombustion exhaust. The sorbent is often activated carbon which iscapable of absorbing or capturing the mercury. Such a sorbent is alsoentrapped by the filtration arrangement 12 and thus part of theparticulate matter 80. Thus again, mercury is entrapped and removed fromthe combustion gas flow. The example system 10 can optionally providefor the use of such a sorbent. However, since there is a mechanism tostop the flow of mercury (i.e., created of mercuric chloride and captureof the created mercuric chloride by particulate matter 80), the use ofsorbent may be minimized or eliminated.

It is to be appreciated that all the examples concerning the filtrationarrangement 12 provide examples of filtration means for removingmaterial, including mercury, from the flow proceeding through thefiltration means.

The ability of the filtration arrangement 12, regardless of themechanism/methodology of removing mercury from the flow, may have anefficiency (i.e., ability to remove the mercury) that is temperaturedependent. For example, it is theorized that the collection of thehydrochloric acid at the filter element of the filtration arrangement12, and/or the oxidation of the elemental mercury by the hydrochloricacid into mercuric chloride and/or the capture of the created mercuricchloride by the particulate matter 80 may vary dependent upontemperature. In other words, the temperature of the combustion exhaustflow that is proceeding through the filtration arrangement 12 may affectthe effectiveness of the mercury removal.

In accordance with an aspect of the present invention, a concentration(e.g., an amount) of mercury within the flow proceeding from thefiltration arrangement 12 (i.e., after the filtration arrangement 12 hashad an opportunity to remove mercury) is sensed. A mercury continuousemission monitoring system (HG CEMS) 84 is an example sensor arrangementfor sensing mercury is schematically shown within the example of FIG. 1and is operatively connected 86 to sense the post-filter combustionexhaust flow proceeding from the filtration arrangement 12. The sensorarrangement provides, as an output, a signal 88 indicative of the sensedmercury concentration.

In accordance with an aspect of the present invention, the temperatureof the flow (i.e., with the combustion exhaust) proceeding to thefiltration arrangement 12 is changed. The change in temperature is forthe purpose of changing the effectiveness of the mercury removal that isoccurring at the filtration arrangement 12. In accordance with an aspectof the present arrangement, the change of the temperature is in responseto the sensed mercury concentration signal 88.

The HG CEMS 84 may have any one or more systems/sensors that can detectand measure the concentration (e.g., amount) of mercury within the flowproceeding from the filtration arrangement 12. It is to be appreciatedthat the specific location of the HG CEMS 84 need not be a specificlimitation upon the invention and that thus the sensor arrangement canbe located anywhere downstream from the filtration function. Forexample, the HG CEMS 84 can be within the clean air plenum 20 of thebaghouse 14, as/at a separate unit outside of the baghouse 14 (as shownwithin the example of FIG. 1), or even downstream of some othercomponent(s) (not shown) in the path that the flow proceeds along toeventual discharge to ambient atmosphere (e.g., via a stack or possiblethough other equipment such as further pollution processing equipment).

The signal 88 conveys information of the sensed mercury concentration.The signal can be of any form. For example, the signal can be an analogor a digital electrical signal. The signal can convey information is anyformat. For example, the mercury concentration information can berepresented via an electrical property (e.g., current or voltage) of asignal or conveyed by a numeric value representation within the signal(e.g., a code). It is to be appreciated that the signal 88 is shown as aschematic representation and that the signal can be conveyed via ahardwired connection, wireless link, or other connection/link. Insummary, the HG CEMS 84, which may have any one or more sensors that canmeasure the concentration (e.g., amount) of mercury within the flowproceeding from the filtration arrangement 12, provide examples ofsensor means for sensing a mercury concentration within the flowdownstream of the filtration arrangement and for providing a signalindicative of the sensed mercury concentration.

As an example to provide one or more of the aspects of the invention,the example system of FIG. 1 includes a temperature control arrangement90 that can change a temperature of the combustion exhaust proceeding tothe filtration arrangement 12. The temperature control arrangement 90may include one or more elements/structures for cooling the combustionexhaust and the temperature control arrangement 90 may include one ormore elements/structures for heating the combustion exhaust. Theelements/structures may even selectively provide both cooling andheating. The specific details of the elements/structures need not bespecific limitations upon the present invention.

One example approach for cooling includes a spraying-introduction offine water mist into the combustion exhaust. As another alternative,relatively cooler, ambient air is introduced to mix with the combustionexhaust. Such examples for cooling the combustion exhaust are examplesof means for cooling the combustion exhaust. An example approach forheating includes employing electrical heating coils to warm thecombustion exhaust. Such an example for heating the combustion exhaustis an example of means for heating the combustion exhaust. It is to beappreciated that adjustment of the temperature may include cooling orheating. However, typically cooling of the combustion exhaust is thedesired course of action.

The temperature control arrangement 90 is operatively connected/arrangedto receive the signal 88 indicative of the sensed mercury concentrationfrom the HG CEMS 84. The change in temperature caused by the temperaturecontrol arrangement 90 is in response to the signal 88 indicative of thesensed mercury concentration. Thus, if there is a desire to capture(entrap) more (or less) mercury, the temperature is changed. Asmentioned, the entrapment of mercury at the filtration arrangement 12 istemperature dependent. The system 10 can be set-up as an automaticfeedback loop in which the temperature of the dirty flue gas enteringthe baghouse 14 of the filtration arrangement 12 is adjusted in responseto the mercury concentration in the exiting flow.

It is to be appreciated that all the examples concerning the temperaturecontrol arrangement 90 provide examples of temperature control means forchanging a temperature of the combustion exhaust proceeding to thefiltration arrangement in response to the signal indicative of thesensed mercury concentration.

It is to be appreciated that the specific location of the temperaturecontrol arrangement 90 need not be a specific limitation upon theinvention and that thus the temperature control arrangement 90 can belocated anywhere upstream of the filtration function or even inconjunction with the filtration function. For example, the temperaturecontrol arrangement 90 can be a separate unit outside of the baghouse 14(as shown within the example of FIG. 1), within the baghouse (e.g.,within the dirty air plenum), or even upstream of some othercomponent(s) (not shown) in the path that the flow proceeds toward thefiltration arrangement 12.

As mentioned, some particulate matter 80 is accumulated on the outersurface 54 the filter media 40 of the filter media. The presence of theparticulate matter 80 helps in entrapment of mercury. It is to beappreciated that the particulate matter 80 may include fly ash from thecombustion exhaust. It is to be appreciated that the particulate matter80 may include introduced sorbent (e.g., activated carbon). Such sorbentmay be injected by an arrangement that is not shown with the example ofFIG. 1. It is to be appreciated that accumulation of particulate matter80 may be due to a geometry (e.g., pleats 48) of the filter cartridge30. Also, it is to be appreciated that some filter materials (e.g.,ePTFE) may enhance an ability to of the arrangement to entrap mercury.

It is worth noting that while the introduction or injection of a sorbent(e.g., activated carbon) into combustion exhaust certainly has apotential benefit of aiding to capture mercury, the introduction of sucha sorbent may have consequences. In particular, the introduced sorbentmay mix with the fly ash that is being captured by the filtrationarrangement 12. It should be noted that fly ash may have value as abyproduct of the filtration of the combustion exhaust. For example, flyash may be sold for use in production of cement. However, the presenceof sorbent (e.g., activated carbon) within the fly ash may have aconsequence of rendering the fly ash to be less desirable for use insuch cement production. Thus, the use of activated carbon may have aconsequence of reduced revenues that may have been generated from thecollection and sale of fly ash. Moreover, activated carbon itself has acost of acquisition. It is easily understood that the overall cost ofthe activated carbon is proportional to amount of activated carbon thatis utilized. Thus, it might be beneficial to reduce sorbent use. Thepresent invention may provide such benefits.

Within one example in which sorbent (e.g., activated carbon) was notinjected (i.e., the particulate for capture of mercuric chloride at thesurface area of the ePTFE membrane layer 76 was only the fly ash), amercury capture rate of approximately 98 percent was achieved when thecombustion exhaust entering the baghouse 14 was cooled to 280° F.(approximately 138° C.). In comparison, a typical temperature forcombustion exhaust entering the bag house is around 345° F.(approximately 174° C.). Thus, in such an example, the need for sorbentis greatly reduced or possibly eliminated.

Also, since the use of measured (monitored) mercury is used, in afeedback approach, to control temperature via the temperature controlarrangement 90, the adjustments (i.e., changes) to the temperature canbe done in a real-time approach. Specifically, the temperature of thecombustion exhaust can continuously be adjusted and/or thecooling/heating applied to the combustion exhaust can be adjusted tomaintain a desired temperature of the combustion exhaust. It is possiblethat the mercury within the combustion exhaust can vary over time. Suchmercury variation may be due to one or more factors. Possible examplesof such factors include variations in the amount/type of fly ash in thecombustion exhaust, gas chemistry within the combustion exhaust,combustion exhaust gas flow rate, filter media condition (e.g.,deterioration thereof), dust-cake build-up, etc. One aspect of thepresent invention is to be able to make a responsive adjustment, via thetemperature adjustment, to cause a change is mercury capture (e.g.,removal from the flow of the combustion exhaust). The adjustment can becontinuous and/or repetitive.

FIG. 5 is a top level flow chart for an example method 100 in accordancewith the present invention. Although the flow chart presents methodsteps in a linear sequence, it is to be appreciated that the steps mayactually be done continuously and simultaneously. The linear sequencepresentation is merely to present the method steps in a manner for easeof understanding. At step 102, the combustion exhaust is passing throughthe filtration arrangement. At step 104, the post-filtered flow issensed to measure the mercury that is present. At step 106, it isdetermined if the mercury is at a desired level. If the sensed mercuryis at a desired level (the answer to the determination at step 106 isYES), the method 100 loops so that steps 104 and 106 are simplyrepeated. However, if the sensed mercury is not at a desired level (theanswer to the determination at step 106 is NO), the method 100 proceedsto step 108 in which the temperature of the combustion exhaustproceeding toward the filtration arrangement is adjusted. It should benoted that the temperature adjustment may include reducing or increasingthe temperature. It should also be appreciated that the method mayinclude other steps and/or the presented steps may include sub-steps.

In summary, the present invention can provide a system for improvedmercury removal from a flow containing combustion exhaust. The systemincludes a filtration arrangement through which the flow proceeds toremove material, including mercury, from the flow. The system includes asensor arrangement sensing a mercury concentration level within the flowdownstream of the filtration arrangement and providing a signalindicative of the sensed mercury concentration. The system includes anadjustable temperature control arrangement changing a temperature of thecombustion exhaust proceeding to the filtration arrangement in responseto the signal indicative of the sensed mercury concentration.

The system may further include that the adjustable temperature controlarrangement includes at least a cooler to cool the combustion exhaustand/or the adjustable temperature control arrangement includes at leasta heater to heat the combustion exhaust. The system may further includethat the sensor arrangement includes at least a sensor that measureswhether the mercury concentration within the flow downstream of thefiltration arrangement is at a desired concentration and the adjustabletemperature control arrangement operates to change the temperature ofthe combustion exhaust such that the mercury removal at the filtrationarrangement changes and the mercury concentration within the flowdownstream of the filtration arrangement changes toward the desiredconcentration. The system may further include that the filtrationarrangement includes at least one layer of ePTFE.

Also in summary, the present invention can provide a system for improvedmercury removal from a flow containing combustion exhaust. The systemincludes filtration means for removing material, including mercury, fromthe flow proceeding through the filtration means. The system includessensor means for sensing a mercury concentration within the flowdownstream of the filtration means and for providing a signal indicativeof the sensed mercury concentration. The system includes temperaturecontrol means for changing a temperature of the combustion exhaustproceeding to the filtration means in response to the signal indicativeof the sensed mercury concentration.

The system may further include that the temperature control meansincludes means for cooling the combustion exhaust and/or the temperaturecontrol means includes means for heating the combustion exhaust. Thesystem may further include that the sensor means includes at least asensor that measures whether the mercury concentration within the flowdownstream of the filtration means is at a desired concentration and theadjustable temperature control means operates to change the temperatureof the combustion exhaust such that the mercury removal at thefiltration means changes and the mercury concentration within the flowdownstream of the filtration means changes toward the desiredconcentration. The system may further include that the filtration meansincludes at least one layer of ePTFE.

Also in summary, the present invention can provide a method for improvedmercury removal from a flow containing combustion exhaust. The methodincludes filtering the flow to remove material, including mercury, fromthe flow proceeding through a filtration arrangement. The methodincludes sensing a mercury concentration within the flow downstream ofthe filtration arrangement and for providing a signal indicative of thesensed mercury concentration. The method includes changing a temperatureof the combustion exhaust proceeding to the filtration arrangement inresponse to the signal indicative of the sensed mercury concentration.

The method may further include that the step of changing a temperatureof the combustion exhaust includes cooling the combustion exhaust. Themethod may further include that the step of changing a temperature ofthe combustion exhaust includes heating the combustion exhaust. Themethod may further include that the step of sensing a mercuryconcentration includes sensing whether the mercury concentration withinthe flow downstream of the filtration arrangement is at a desiredconcentration and the step of changing a temperature of the combustionexhaust includes changing the temperature of the combustion exhaust suchthat the mercury removal at the filtration arrangement changes and themercury concentration within the flow downstream of the filtration meanschanges toward the desired concentration. The method may further includethat the step of filtering the flow to remove material filtrationincludes filtering though at least one layer of ePTFE.

The invention has been described with reference to the exampleembodiments described above. Modifications and alterations will occur toothers upon a reading and understanding of this specification. Examplesembodiments incorporating one or more aspects of the invention areintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims.

What is claimed is:
 1. A system for improved mercury removal from a flowcontaining combustion exhaust; the system including: a filtrationarrangement through which the flow proceeds to remove material,including mercury, from the flow; a sensor arrangement sensing a mercuryconcentration within the flow downstream of the filtration arrangementand providing a signal indicative of the sensed mercury concentration;and an adjustable temperature control arrangement changing a temperatureof the combustion exhaust proceeding to the filtration arrangement inresponse to the signal indicative of the sensed mercury concentration tochange an amount of mercury being removed from the flow.
 2. A system asset forth in claim 1, wherein the adjustable temperature controlarrangement includes at least a cooler to cool the combustion exhaust.3. A system as set forth in claim 1, wherein the adjustable temperaturecontrol arrangement includes at least a heater to heat the combustionexhaust.
 4. A system as set forth in claim 1, wherein the sensorarrangement includes at least a sensor that measures whether the mercuryconcentration within the flow downstream of the filtration arrangementis at a desired concentration and the adjustable temperature controlarrangement operates to change the temperature of the combustion exhaustsuch that the mercury removal at the filtration arrangement changes andthe mercury concentration within the flow downstream of the filtrationarrangement changes toward the desired concentration.
 5. A system as setforth in claim 1, wherein the filtration arrangement includes at leastone layer of ePTFE.
 6. A system as set forth in claim 1, wherein theadjustable temperature control arrangement includes at least one of acooler to cool the combustion exhaust and a heater to heat thecombustion exhaust.
 7. A system for improved mercury removal from a flowcontaining combustion exhaust; the system including: filtration meansfor removing material, including mercury, from the flow proceedingthrough the filtration means; sensor means for sensing a mercuryconcentration within the flow downstream of the filtration means and forproviding a signal indicative of the sensed mercury concentration; andtemperature control means for changing a temperature of the combustionexhaust proceeding to the filtration means in response to the signalindicative of the sensed mercury concentration to change an amount ofmercury being removed from the flow.
 8. A system as set forth in claim7, wherein the temperature control means includes means for cooling thecombustion exhaust.
 9. A system as set forth in claim 7, wherein thetemperature control means includes means for heating the combustionexhaust.
 10. A system as set forth in claim 7, wherein the sensor meansincludes at least a sensor that measures whether the mercuryconcentration within the flow downstream of the filtration means is at adesired concentration and the adjustable temperature control meansoperates to change the temperature of the combustion exhaust such thatthe mercury removal at the filtration means changes and the mercuryconcentration within the flow downstream of the filtration means changestoward the desired concentration.
 11. A system as set forth in claim 7,wherein the filtration means includes at least one layer of ePTFE.
 12. Asystem as set forth in claim 7, wherein the temperature control meansincludes at least one of means for cooling the combustion exhaust andmeans for heating the combustion exhaust.
 13. A method for improvedmercury removal from a flow containing combustion exhaust; the methodincluding: filtering the flow to remove material, including mercury,from the flow proceeding through a filtration arrangement; sensing amercury concentration within the flow downstream of the filtrationarrangement and for providing a signal indicative of the sensed mercuryconcentration; and changing a temperature of the combustion exhaustproceeding to the filtration arrangement in response to the signalindicative of the sensed mercury concentration to change an amount ofmercury being removed from the flow.
 14. A method as set forth in claim13, wherein the step of changing a temperature of the combustion exhaustincludes cooling the combustion exhaust.
 15. A method as set forth inclaim 13, wherein the step of changing a temperature of the combustionexhaust includes heating the combustion exhaust.
 16. A method as setforth in claim 13, wherein the step of sensing a mercury concentrationincludes sensing whether the mercury concentration within the flowdownstream of the filtration arrangement is at a desired concentrationand the step of changing a temperature of the combustion exhaustincludes changing the temperature of the combustion exhaust such thatthe mercury removal at the filtration arrangement changes and themercury concentration within the flow downstream of the filtration meanschanges toward the desired concentration.
 17. A method as set forth inclaim 13, wherein the step of filtering the flow to remove materialfiltration includes filtering though at least one layer of ePTFE.
 18. Amethod as set forth in claim 13, wherein the step of changing atemperature of the combustion exhaust includes at least one of coolingthe combustion exhaust and heating the combustion exhaust.